1. Field of the Invention
Exemplary aspects of the present invention generally relate to an image forming apparatus such as a copier, a facsimile machine, or a printer.
2. Description of the Background
Related-art image forming apparatuses typically form a toner image on a recording medium (e.g., a sheet) according to image data using an electrophotographic method. In such a method, for example, a charger charges a surface of a latent image bearing member (e.g., a photoconductor); an irradiating device emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data; a developing device develops the electrostatic latent image with a developer (e.g., toner) to form a toner image on the photoconductor; a transfer device transfers the toner image formed on the photoconductor onto a sheet; and a fixing device applies heat and pressure to the sheet bearing the toner image to fix the toner image onto the sheet. The sheet bearing the fixed toner image is then discharged from the image forming apparatus.
A temperature within the image forming apparatuses is usually increased due to heat generated by the irradiating device, the developing device, the fixing device, and so forth.
For example, in the developing device, when a developer agitator is driven to agitate and convey developer within the developing device, the temperature within the image forming apparatus is increased due to frictional heat generated by friction between the developer agitator and the developer, and friction within the developer. Further, frictional heat generated by friction between the developer and a developer restriction member (often a doctor blade or the like) that regulates a thickness of the developer borne by a developer bearing member before the developer reaches a developing position inside the image forming apparatus, and friction within the developer occurring with regulation by the developer restriction member also causes an increase in a temperature within the image forming apparatuses.
The increase in temperature of the image forming apparatuses causes a decrease in an amount of charge given the toner in order to form images, thereby increasing an amount of toner attached to the recording medium. Consequently, a predetermined image density cannot be attained. Further, the temperature increase can melt the toner, causing the melted toner to adhere to the developer restriction member, the developer bearing member, the photoconductor, and so forth, possibly causing irregular images having undesired lines as a result. In particular, when recently-used toner having a lower melting temperature is used in an effort to reduce fixing energy, irregular images due to toner adhesion are more likely to occur.
To solve the above-described problems, a technique in which air introduced by an air-cooling fan is conveyed to the developing device and/or a surrounding area through a duct to generate airflow for cooling the developing device has been proposed to prevent an excessive increase in temperature of the developing device. However, recent demands for downsizing of the image forming apparatuses has caused components to be densely packed within the image forming apparatuses, and a space provided around the developing device has been limited. Consequently, it is difficult to provide the duct to convey the airflow to the portion around the developing device, and that makes it difficult to cool the developing device using the above-described technique.
In addition, the following problems arise in the transfer device. Specifically, an intermediate transfer belt included in the transfer device is cleaned by a cleaning blade included in a belt cleaning unit to remove residual toner and so forth from the intermediate transfer belt after transfer. The toner thus removed is collected by a waste toner conveyance unit, and then is accumulated in a waste toner container with other waste toner within the image forming apparatus.
Because the belt cleaning unit is usually positioned near the fixing device and itself generates heat, the temperature of the belt cleaning unit will exceed the melting point of the toner if left as is. In order to prevent an excessive increase in temperature of the transfer device partially contacting the belt cleaning unit, a technique in which air introduced by an air-cooling fan is conveyed to a portion around the transfer device through a duct to generate airflow for cooling the transfer device has been proposed. However, as described above, recent demands for downsizing of the image forming apparatuses has caused components to be ever more densely packed within the image forming apparatuses, and a space provided around the transfer device has been limited. Consequently, it is difficult to provide the duct to convey the airflow to the portion around the transfer device, and that makes it difficult to cool the transfer device using the above-described technique. Further, if the airflow is generated around the transfer device to cool the transfer device, toner scattering may occur within and outside the image forming apparatus.
Published Unexamined Japanese Patent Application No. 2005-164927 (hereinafter referred to as JP-2005-164927-A) discloses an image forming apparatus employing a liquid cooling method in which a liquid is circulated to cool a developing device that generates heat. A liquid cooling device provided in the image forming apparatus includes a heat receiving part contacting a wall of the developing device such that a cooling liquid within the heat receiving part receives heat from the developing device, a radiator serving as heat releasing means to release heat from the cooling liquid, a circulation pipe to circulate the cooling liquid between the heat receiving part and the radiator, and a conveyance pump to convey the cooling liquid within the circulation pipe to the heat receiving part. Because it provides better cooling performance than the air cooling device does, the liquid cooling device can more efficiently cool the developing device compared to the air cooling device. Further, the circulation pipe to circulate the cooling liquid is smaller than the duct described above, so that even those image forming apparatuses having a smaller space around the developing device can include the circulation pipe around the developing device. Accordingly, the developing device provided within the densely-packed image forming apparatus can be efficiently cooled.
In general, the developing device is detachably attachable to the image forming apparatus either directly by itself or indirectly through integration with the photoconductor as a process cartridge. Because the size and stability of a developing gap formed between the photoconductor and the developer bearing member in the developing device considerably influence image quality, the image forming apparatus generally includes positioning means for accurately installing the developing device at a position relative to the photoconductor.
In the image forming apparatus disclosed in JP-2005-164927-A, a contact/separation mechanism is provided such that the heat receiving part is separated from the developing device when the developing device is detached from the image forming apparatus, and the heat receiving part is pressed against the developing device using biasing means to contact the developing device when the developing device is attached to the image forming apparatus, thus facilitating attachment/detachment of the developing device to and from the image forming apparatus.
However, because the heat receiving part is pressed against the developing device using the biasing means when the developing device is attached to the image forming apparatus, a force applied to the developing device from the heat receiving part acts on the positioning means and so forth. Consequently, the positioning means and so forth may be inadvertently deformed, causing a change in the developing gap.
Further, if the liquid cooling method disclosed in JP-2005-164927-A is used to cool the belt cleaning unit, the intermediate transfer belt is not properly cleaned by the cleaning blade when a distance between the intermediate transfer belt and a cleaning blade is inadvertently changed.
For example, when the distance between the cleaning blade and the intermediate transfer belt is larger than a predetermined value, toner remaining on the intermediate transfer belt cannot be reliably removed by the cleaning blade, and the next sequence of transfer operations is performed with the intermediate transfer belt having residual toner thereon. Consequently, image blur and operation shutdown of the transfer device due to clogging of toner may occur.
By contrast, when the distance between the cleaning blade and the intermediate transfer belt is too small, the cleaning blade may curl up, possibly damaging the cleaning blade or the intermediate transfer belt as a consequence.